ABSTRACT: Mucoceles are the structures that are limited in the epithelium and are filling in the paranasal sinuses with mucus content. They are most frequently seen in the frontal sinus and then in ethmoid, maxillary and sphenoid sinuses, by decreasing rate. They cause bone erosion as they enlarge and different symptoms when they run over the sinus. Left orbital pain, periorbital edema and proptosis was determined in the examination of the 43 years old male patient; who was referred to our clinic with progressively enlarging left orbital tumour for seven months. In the paranasal sinus computerized tomography, a mucocele; approximately with the diameter of 3x1, 5x3,5 cm, that fills in the whole frontal sinus and reachs the orbita by eroding the inferior sinus wall and compresses the orbita superiorly, was determined. This frontal sinus mucocele was marsupialized to the nasal cavity by endoscopic sinus surgery.

Key Words: Mucocele, frontal sinus, proptosis